Filter made from powdered metal

ABSTRACT

A metallurgically integral filter comprising sintered laminae of shaped powdered metal, said laminae comprising an impervious structural member, a filter element, and a pervious support member sandwiched between said structural member and said filter element, with a drainage space between said structural member and said pervious support member. A series of such sintered filters can be stacked within a housing in spaced relation with the drainage areas of said filters communicating with a discharge pipe, to form a filter assembly useful in removing solid particles from liquids or gases.

United States Patent [1113,581,902

[72] Inventor James L. Bidler [56] I ReierencesCited Lake Elmo, Milm-UNITED STATES PATENTS g Q J' zff'a g 2,978,108 4/1961 Strassheim2l0/488X N 1971 2,997,777 8/1961 Davies 210/s10x 1 'F" n dM f 3,294,24112/1966 SicardetaL. 21o/347x [73] xgg 3,294,242 12/1966 Notari 210/347St. Paul, Minn. Primary ExaminerJ. L. Decesare Attorney- Kinney,Alexander, Sell, Steldt & Delahunt ABSTRACT: A metallurgically integralfilter comprising sintered laminae of shaped powdered metal, saidlaminae com- FILTER MADE FROM POWDERED METAL prising an imperviousstructural member, a filter element, and

6 Claims 7 Drawing a pervious support member sandwiched between saidstructural member and said filter element, with a drainage space [52][1.8. CI 210/347, between said structural member and said pervioussupport 210/486, 210/496, 210/510 member. A series of such sinteredfilters can be stacked within [51] Int. Cl BOld 25/02 a housing inspaced relation with the drainage areas of said fil- [50] Field ofSearch 29/4205; ters communicating with a discharge pipe, to form afilter as- 210/486, 488, 455, 457, 350, 347, 496, 510 sembly useful inremoving solid particles from liquids or gases.

FILTER MADE FROM POWDEREI) METAL 1. Field of the Invention The inventionrelates to filters made from sintered powdered metals, and to a processfor making such filters.

2. Background of the Prior Art Filter assemblies comprising a pluralityof filter leaves with filter elements made of paper, cloth, or wovenwire screens supported by a structural member of some type, with aninternal drainage area, are old in the art (see for example U.S. Pat.Nos. 1,726,035, 2,249,063, 2,423,547, and 2,444,147). Due to vibrations,pressures, and other stresses and forces arising during operation, suchfilter leaves often deform, rupture, or otherwise fail because of theirinadequate strength, even when supported, for example, with coarserscreens or structural cores. Screens, themselves, are expensive anddifficult to manufacture and clean. Improved filter leaves of greaterstrength and capable of filtering small particles have been disclosedmade from sintered powdered metal, using powder metallurgy techniques(see, for example, U.S. Pat. Nos. 2,267,918, 2,293,843, 2,430,078,2,462,045, 2,463,825, 2,554,343, 2,593,943, 2,909,363, 2,997,777,3,049,795, 3,152,988, 3,201,858, 3,230,618, 3,241,681, and 3,359,622).However, these prior art powder metal filters have one or moredisadvantages, such as requiring the use of expensive specially gradedpowdered metals, or requiring relatively thick filter elements to obtainneeded strength at the sacrifice of flow rate or throughput, orrequiring welding, brazing, or mechanical fastening of porous metalparts to wrought parts, or the use of incompressible structural coresagainst which the filter elements are liable to be compressed underpressure with consequent decrease in flow rate, or requiring densifyingpressing operations in fabricating the filter elements.

BRIEF SUMMARY OF THE INVENTION The filter leaf of this invention isentirely made of sintered powdered metal to form an integral rigidstructure which does not have shortcomings of prior art filters made ofpowdered metal. Briefly, the filter leaf of this invention ismetallurgically integral and comprises sintered laminae of shapedpowdered metal, the laminae broadly comprising an impervious structuralmember, a filter element, and a pervious support member interposed orsandwiched between said structural member and said filter element, witha drainage space or area between said structural member and said filterelement, said drainage space preferably communicating with a dischargepipe. The term metallurgically integral" as used herein means that thecontiguous surfaces of the filter leaf components are bonded together byinteratomic diffusion, as a result of the sintering of the assembly, thesintered filter leaf thus in effect being one piece of metal. In apreferred embodiment, the filter leaf before sintering comprises alaminae of five discs of green, dried, compacted powdered metal with theperipheral edges of the discs sealed with a ring of green undriedpowdered metal. After being so-assembled, the whole assembly is sinteredas a unit to form a metallurgically integral rigid filter leaf. Themiddle or center disc serves as a structural core and it issubstantially impervious and has on its two faces an array of spacedapart protuberances, such as studs integral with the core. Each of thefiltering elements is supported by a relatively more permeable supportdisc of powdered metal which is interposed or sandwiched between thefiltering element and the protuberances or studs. The spaces between thecore and abutting support members form a drainage space or area whichcommunicates with a central opening passing through the assembly. Aseries of such sintered filter leaves can be stacked in spaced relation,for example, by interposing separator rings between filter leaves, on adischarge pipe or channeled rod passing through the central openings ofthe series, and the stack mounted within a housing to form a filterassembly useful in removing solid particles from liquids or gas.

DRAWING In the accompany drawing, there is illustrated a preferredembodiment of this invention. FIG. 1 is an exploded isometric view of afilter leaf of this invention before it is assembled and sintered. FIG.2 is a sectional view in elevation of a sintered filter leaf or thisinvention. FIG. 3 is an enlarged sectional view of the peripheralportion of the filter leaf of FIG. 2. FIGS. 4 and 5 are side elevationalviews of a discharge rod upon which a plurality of the sintered filterleaves of FIG. 2 can be mounted. FIG. 6 is a sectional view of FIG. 5taken along the plane 6-6 indicated. FIG. 7 is an elevational view inpartial section of a filter assembly in which have been mounted a seriesor stack of the filter leaves of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the accompanyingdrawing, and initially to FIG. 1, reference number 111 designates acircular or disclike green structural core of shaped powdered metal, thetwo faces of which are provided with a plurality of integralprotuberances or studs 12 (only a portion of which are shown forbrevity), the core having a central opening 13. Members 14 and 16 arecircular or disclike green filter elements or media, having a smoothplanar face and central openings 17 and 18, respectively. Disposedbetween core 11 and filter elements 14 and 16 are two circular greendisclike supports 19 and 21, which also have planar faces and centralopenings 22 and 23, respectively. Supports l9 and 21 have outsidediameters smaller than core 11 and filter elements 14 and 116 toaccommodate seal rings 15 and 20 within which the supports are to bedisposed, these rings being made of green, undried powdered metal. Byapplying a light but sufficient pressure to the top and bottomperipheral portions of the assembly, the seal rings 15 and 20 will besqueezed or extruded around the periphery of the discs to seal the edgeof the assembly as shown in detail in FIG. 3.

FIGS. 2 and 3 illustrate the filter leaf of FIG. 1 as assembled andsintered, the contiguous parts of the various discs beingmetallurgically bonded as a result of the sintering to form an integralrigid unit, generally designated 25, the several central openings ofeach of these components forming a common central opening 24 with theinternal filtrate drainage areas being designated by reference number26. The peripheral edges of the discs are also metallurgically bonded bya ring 27 resulting from the pressing of rings 15 and 20, as describedabove. When a plurality of these filter leaves 25 are assembled, theyare held in spaced relation by spacer rings 28 disposed on each side ofeach of the filter leaves. Such spacer rings have a central opening 29of the same diameter of openings l3, l7, 18, 22 and 23 after theassembly has been sintered.

A series of filter leaves 25 can be mounted on a discharge rod or shaftgenerally designated 31 illustrated in FIGS. 4, 5 and 6. The outerdiameter of rod 31 is such that the stack of filter leaves can be snuglymounted thereon. The outer surface of the discharge rod 311 has aplurality of longitudinally aligned channels 32 which progressivelyincrease in depth toward the bottom of the rod, such channels being incommunication with the drainage areas 26 of the series of filter leaves25 mounted on the rod. The lower ends of channels 32 communicate viapassages 30 with a common drain area 35 in the bottom of the rod 31, thelower end of which is threaded at 48 and the upper end being providedwith a tapped hole 50.

Referring to FIG. 7, a filter assembly is shown comprising a cylindricalhousing or casing 34 surmounted by a top cover or cap 36 which can befastened thereto by means of bolts 37 or the like. Surrnounting cap 36is a flange 38 provided with inlet port or passage 39. The lower end ofcasing 34 is mounted on a supporting bottom closure or baseplate 41 andfastened thereto by means of bolts 42 or the like. Baseplate 41 has alower flange portion 43 with a discharge port or passage 44 therein. Asassembled, casing 34 with its top cap 36 and baseplate 41 define aninternal chamber 46 which communicates at its upper end with inletpassage 39 to receive liquid or gas laden with solid particles or thelike which are to be separated or filtered. Centrally disposed withinchamber 46 is a series of stacked filter leaves 25 of FIG. 2, thisassembly being generally designated as 47. The lower threaded end 48 ofdischarge rod 31 is threaded into a tapped hole provided in the upperportion of baseplate 41, so as to support assembly 47 within chamber 46,the lower-most spacer ring 28 of the assembly resting on an internalcentral shoulder of baseplate 41. The upper threaded hole 50 ofdischarge rod 31 is threadedly connected to a nipple 49, which in turnis threadedly connected at 51 to a distributor cap 52 which surmountsassembly 47,- the distributor cap serving to distribute around suchassembly the solid-laden liquid or gas introduced via passage 39.Surrnounting the series of stacked filter leaves, and the uppermostspacer ring 28", is a retaining ring or collar Means such as pipes orthe like for supplying the solid-laden material to be filtered and forwithdrawing the filtered material are conventional and are not shown inthe drawing in the interest of brevity. Further, the filter assembly canbe supported by any conventional means in an upright position, forexample, by legs or a platform. Where it is desirable to maintain thematerial being filtered in a heated state, the outer wall of theassembly can be provided with conventional electrical heating bands 54or the like.

As mentioned hereinbefore, the entire filter leaf of this invention ismade from sintered powdered metals using, in part, conventional powdermetallurgy techniques. An excellent description of this metallurgicalprocess is found in Review of the Powder Metallurgy Process," July,1966, published by the U.S. Army Production Equipment Agency,Manufacturing Technology Division, Rock Island Arsenal, Illinois. Alsosee U.S. Pat. No. 3,367,752.

The preferred powdered metals used in this invention are those ofaustenetic chromium-nickel stainless steel, these alloys generallycontaining 16.0 to 26.0 weight percent chromium, 6.0 to 22.0 weightpercent nickel, 0.03 to 0.25 weight percent carbon, and occasionallysome other elements added to develop certain specific properties, suchas 1.75 to 4.00 weight percent molybdenum or small amounts of titanium,tantalum, and niobium to minimize formation of chromium carbides,especially in welding. Standard types of these steels have been assignednumbers and specifications by the American Iron and Steel Institute.These are generally known in the art as stainless steels of the AISI 300series, types 301, 302, 304 and 305 generally referred to as 188stainless steel, and the workhorse" type 316 generally referred to as18-8 Mo." All of these AISI stainless steels of the 300 series areapplicable in the practice of this invention. Of course, other powderedmetals can be used in fabricating the filter leaves of this invention,such as nickel, tungsten, copper, and the like, and alloys of suchmetals, including bronze, monel, etc.

In making the structural core of the filter leaf, the particle size ofthe powdered metal should be fine enough so that the resulting shapedstructural core, upon sintering, will be relatively strong andimpermeable. For this purpose, a particle size of 325 mesh is preferred.The filter elements are made from powdered metal which is relativelycoarse in order, upon sintering the resulting shaped disc, to obtain thedesired permeability or micronic rating. The support disc or backup forthe filter element is made from powdered metal which is relativelycoarser than that used to make the filtering elements. For purposes ofmaking the filter elements and supports, mesh sizes in the range of50+325 can be used, such as 200+325, l+200, 50+l00, or blends thereof,suitably selected to produce the desired micronic rating or bubblepoint, and to that end small amounts of, e.g., l20 weight percent of 325mesh can be blended with the coarse powder, i.e., with the 50+325 mesh.(The term "mesh" referred to herein means mesh size according to U.S.Standard Sieve.) The use of powdered metal With these mesh ranges willenable one to make filter leaves in accordance with this invention withvarious micronic ratings, e.g., in the range of l to 150 microns.

In fabricating each of the filter leaf components, the powdered metal ofdesired mesh is blended with an organic heatfugitive binder, such asthose disclosed in U.S. Pat. Nos. 2,593,943, 2,709,651, and 2,902,363;the preferred binder is methyl cellulose. Various solvents can be usedin conjunction with these binders, such as water, as well as variousplasticizers, such as glycerin. The blending can be carried out in aconventional manner in various types of commercially available mixers,blenders, tumblers, and the like, care being taken to insure that theblend is homogeneous and the components well dispersed. The resultingblend will be in the nature of a plastic mass or dough and will besimilar in consistency to that of modeling clay. The plastic mass can beshaped on a rubber mill, calendared, or knife-coated to the desiredthickness and then dried to form a green sheet having a leathery nature.In the case of the structural member or core, the green sheet can besuitably embossed or otherwise shaped to form the protuberances or studsnecessary to provide the drainage area for the filter leaf. The greensheets can then be cut to size, taking into account the l25 percentlinear shrinkage which will occur upon sintering and compensating for itby cutting the shapes with oversize dimensions.

The green components forming the laminae of the filter leaf areassembled in the proper contiguous relation using suitable fixtures anddies. The binder is reactivated by addition of solvent or l3 percentsolution of binder in solvent and the entire assembly is pressed lightlyto cohere the laminae and extrude the sealing rings into place andthereby produce a coherent integral green structure. This integral greenstructure is then sintered under vacuum or a suitable atmosphere, suchas a reducing atmosphere like hydrogen or dissociated ammonia. Sinteringatmosphere, temperature, and duration of sintering will depend upon theparticular powdered metals used, the selection of these conditions beingwithin the skill of the art. In the case of the austenetic stainlesssteels mentioned above, a hydrogen or dissociated ammonia atmospherewith a dew point of 40 F. or lower and sintering temperatures in therange of l,200 to l,400 C., preferably l,250 to l,350 C., will besuitable, and the duration of sintering will usually be from 10 minutesto 2 or 3 hours.

As is evident from the above, the filter leaf of this invention is madeentirely from powdered metals without requiring or employing wroughtmetal components. The filter leaf is constructed without welding and is,therefrom, free of the disadvantages associated with welding or othermeans of fastening. Fabrication of the filter leaf does not require theuse of specially graded metal powders and does not depend upon thethickness of the filter element for its density or strength;consequently, the filter element can be designed to optimize theporosity and flow characteristics. An important advantage or feature ofthe filter leaf of this invention is the integral metallurgical orsinter bond between the various laminae, each of which serves severalfunctions without hampering the integrity of the entire filter leaf,this feature enabling the filter leaf to withstand stresses and otherforces normally encountered during operation without being prone to thedeformation, rupture, or other types of failure experienced with priorart filters of powder metal which do not have the metallurgicallyintegral supported features of this invention. This construction alsowill withstand reverse flow conditions and back-flushing cleaningoperation without the likelihood of failure. Higher operating pressurescan be used without ear that the filter element will be deformed againstthe supporting core and result in loss of effective filtering area anddrainage by virtue of pressure sealing of the filter element against thestructural core, which is commonly found where the support used for thefilter element is a woven wire screen. The drainage area of the filterleaf has the advantage of simplicity of construction over prior artdevices which depend upon the use of a screen or a volatilized orleached pathway. Since the uniformity and density of the green sheetsused to make the various laminae of the filter leaf of this inventioncan be closely controlled to a high degree of dimensional tolerance, andbecause it is not necessary to extrude, roll, or otherwise work theassembled laminae, high dimensional control is achieved in the finalsintered article.

In another aspect of this invention. the support member (e.g., items 19and 21 in FIG l)sandwiched between the filter element and structuralmember, is fabricated from a green sheet comprising a blend of powderedferrite stabilizer (e.g., molybdenum) and powdered austeniticchromium-nickel stainless steel, as described in copending applicationSer No. 743,588, filed July l0, i968, by T. R. Bergstrom. When thissupport member is sintered as part of the assembled filter leaf, itforms at 1,250 1 ,350C C. an essentially two-phase structure ofaustenite and ferrite, having high tensile strength, thereby enhancingthe overall strength of the filter leaf. Also, making the support memberfrom this blend of austenitic stainless steel and ferrite stabilizerwill enable one to make a thinner support element at equivalent strengththan if only stainless steel powder is used, and the thinner the supportmember (without sacrifice in strength) the more filter leaves one canput in a filter housing and the greater the capacity or throughput ofthe filter. Further details concerning the fabrication of this supportmember will be omitted in the interest of brevity and reference to saidcopending application Ser. No. 743,588 is made for that purpose, thedisclosure of which is incorporated herein. The filter element and/orthe structural member or core can also be made of the blend ofaustenitic stainless steel and ferrite stabilizer if additional strengthis desired.

EXAMPLES The object and advantages of this invention are furtherillustrated by the following examples, but the particular materials andamount thereof recited in this example, as well as other conditions anddetails, should not be construed to unduly limit this invention.

A center structural core was made by mixing 3,200 grams of 325 meshstainless steel powder (Anchor 316 L), 150 grams of 4,000 cps. methylcellulose (Methocel), and 410 ml. of a volume percent solution ofglycerin in water, in a Braebender sigma blade mixer for 1 hour, afterwhich the material had the consistency of modeling clay. The claylikematerial was then formed into a sheet 0.125-inch thick by passing itthrough a rubber mill. After drying for 24 hrs. at room temperature, the

green sheet was placed between two 1/] 6-inch thick perforated metalplates, having 9/64-inch round, staggered holes at 3/16-inch centers,and pressed until the material filled the holes in the perforated sheetto form an array of studs one-sixteenth inch in height. The perforatedplates were removed and a 7.50-inch disc with a 2.00-inch center holewas cut from the studded green sheet using a suitable die.

The intermediate, large pore size, support discs were made from amixture of 2,850 grams of 50+l00 mesh 3161. stainless steel powder(Anchor 3161.), l50 grams of molybdenum powder (Fisher No. of about 4microns), 150 grams of 4,000 c.p.s. methyl cellulose, and 650 ml. of a15 volume percent solution of glycerine in water, in a sigma blade mixerfor one hour, at which time the material had the consistency of modelingclay. A sheet 0.050-inch thick was made by passing the material througha rubber mill, after which the sheet was dried at room temperature, and7.25-inch diameter discs with a 2.00-inch center hole were cut from thesheet using a suitable die.

The filter elements were made by mixing 2,400 grams of -l00+200 mesh and600 grams of 325 mesh 316L stainless steel powder (Anchor 3161.), 150grams of 4,000 c.p.s. methyl cellulose, and 525 ml. of a 15 volumepercent solution of glycerine in water, in a sigma blade mixer. Theresulting claylike material was sheeted, dried, and cut into 7.50-inchdiameter, 0.035-inch thick discs with a 2.00-inch center hole in thesame manner as the support disc described above.

Both faces of the center structural disc and the intermediate supportdiscs, and the inner face of the filter element discs were wetted with al weight percent solution of 4,000 c.p.s. methyl cellulose in water andstacked in the proper order (see FIG. 2) over a 2.00-inch post. Anextruded rod, made by forcing the undried, claylike 325 mesh stainlesssteel through a 0.300-inch die, was shaped in the form of a ring arounda ll8- inch peripheral portion of both sides of the center structuralcore before the intermediate support and outer filter element discs werepositioned. The resulting assembly was compressed around the outerperipheral portion, using a pressing and retaining ring, to force the325 mesh extruded rings over the edge of the inner structural disc. Alldiscs were thereby cohered together using the cohesiveness of the methylcellulose. After room temperature drying, the peripheral portion of theassembly consisted of a 325 mesh bead sealing the edge of the assembly.

The green assembly was placed on an inert sagger and heated slowly tol,350 C. in a hydrogen atmosphere and held for 2 hrs. The resultingsintered filter leaf was an integral composite with all discsmetallurgically bonded together. The filter elements were 0.035-inchthick, 50 percent porous, and had an absolute micronic rating of 20microns. The intermediate support members were 0.050-inch thick, 50percent porous, and had an absolute filtration rating of 65 microns. Thecenter structural core was 0. l inch thick across the embossedprojections and had 0.062 inch of continuous material between theembossed projections. The filter leaf was 7.00 inches in diameter with a1.90-inch hole through the center.

The pressure drop across two of the filter leaves prepared as describedabove was determined by filtering molten viscous polyester and forpurposes of comparison the pressure drop of two commercial prior artfilter leaves made of powdered metal was also determined. Each of theprior art filter leaves comprised an inner stainless steel screensandwiched between two filter elements (supported only by the screen)each measuring 0.062 inches in thickness and 7 inches in diameter andmade from sintered porous sheets of powdered stainless steel. The filterleaf assembly had a weld about its periphery and a machined center hubof wrought steel. These prior art filter leaves had substantially thesame filter area and micronic rating as the filter leaves of thisinvention made as described above. Table 1 sets forth the resets of thiscomparison TABLE I Filter leaves of subject application Prior art filterleaves Number 1 Number 2 Number 3 Number 4 Pres- Pres- Pres- PressureFlow sure Flow sure Flow sure Flow drop, rate drop rate drop, rate drop,rate p.s.i. lb./hr. p.s.i. lhr. p.s.i. b./hr. p.s.i. 1b.,hr.

As the data of Table I show, the pressure drop across the filter leaf ofthis invention is as much as about 2.5 to 3 times less than that acrossthe prior art filter leaf at equal flow rate.

The air permeability of the filter leaf of this invention was 2.8 timesgreater than that of the prior art filter leaf and the flexuralstiffness of the former was 2 to 3 times greater than that of thelatter. Filter leaves made by the teachings of th1s invention were usedto filter a viscous, molten polyester polymer at 550 F. until a maximumpressure differential of 4,500 p.s.i. was reached, with excellentresults.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodiment setforth herein.

lclaim:

1. A metallurgically integral filter leaf of sintered laminae of shapedpowdered metal comprising a substantially impervious structural member,a filter element, and a pervious support member sandwiched between saidstructural member and said filter member, with a drainage space betweensaid structural and support members.

2. A metallurgically integral filter leaf of five jointly sinteredlaminae of powdered metal comprising, in combination a substantiallyimpervious core having a plurality of spaced-apart protuberancesprotruding form each side of said core; pervious support membersdisposed on each side of said core and contiguous with the protuberancesprotruding from said side, thereby forming a drainage space on each sideof said core; and filter elements of less permeability than said supportmembers and disposed on each of the outer sides of said support membersand contiguous therewith; said core, support support members compriseaustenitic chromium-nickel stainless steel and ferrite stabilizer.

5. A filter assembly comprising, in combination: a housing having aninlet and an outlet, with a filtering chamber disposed within saidhousing and in communication with said inlet; a plurality of the filterleaves of claim 1 disposed within said chamber in spaced-apart relationand with the drainage areas of said filter leaves communicating with acommon drainage conduit that communicates with said outlet.

6. A filter assembly comprising, in combination: a housing having aninlet at its upper end and an outlet at its lower end with a filterchamber disposed within said housing and in communication with saidinlet; a plurality of the filter leaves of claim 2 disposed within saidchamber, said filter leaves being mounted in spaced apart relation on adrainage shaft passing through the common central openings of saidfilter leaves, said shaft having drainage channels therein whichcommunicate with said drainage spaces of said filter leaves and whichcommunicates with said outlet.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,581 ,902Dated June 1 1971 Inventor(s) mes L Bldler It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 2, line 19, "disclike" should read disc-like Column 5, line 9,"1,350C.C." should read 1,350 C. Column 6, line 38, "resets" should readresults line 53, 5th column of Table I, "2405" should read 2495 Column7, line 7, "form" should read from Signed and sealed this 21st day ofDecember 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer ActingCommissioner of Patents Column 1, line 22, "2,909,363" should read2,902,363

I FORM PC4050 (10459) USCOMM-DC 60376-P69 9 U 5, GOVRNMENT PRINTINGOFFICE I 1... 035-3!

2. A metallurgically integral filter leaf of five jointly sinteredlaminae of powdered metal comprising, in combination: a substantiallyimpervious core having a plurality of spaced-apart protuberancesprotruding form each side of said core; pervious support membersdisposed on each side of said core and contiguous with the protuberancesprotruding from said side, thereby forming a drainage space on each sideof said core; and filter elements of less permeability than said supportmembers and disposed on each of the outer sides of said support membersand contiguous therewith; said core, support members, and filterelements being shaped in the form of discs with their peripheriesmetallurgically sealed together and having a common central openingwhich communicates with said drainage spaces.
 3. A filter leaf accordingto claim 2, wherein said powdered metal comprises austeniticchromium-nickel stainless steel.
 4. A filter leaf according to claim 3,whereiN said pervious support members comprise austeniticchromium-nickel stainless steel and ferrite stabilizer.
 5. A filterassembly comprising, in combination: a housing having an inlet and anoutlet, with a filtering chamber disposed within said housing and incommunication with said inlet; a plurality of the filter leaves of claim1 disposed within said chamber in spaced-apart relation and with thedrainage areas of said filter leaves communicating with a commondrainage conduit that communicates with said outlet.
 6. A filterassembly comprising, in combination: a housing having an inlet at itsupper end and an outlet at its lower end with a filter chamber disposedwithin said housing and in communication with said inlet; a plurality ofthe filter leaves of claim 2 disposed within said chamber, said filterleaves being mounted in spaced apart relation on a drainage shaftpassing through the common central openings of said filter leaves, saidshaft having drainage channels therein which communicate with saiddrainage spaces of said filter leaves and which communicates with saidoutlet.